1. Field of the Invention
The present invention relates to a passenger detecting system, a passenger detecting method and an air bag system using the same. More particularly, the present invention relates to the technique for detecting an existence or non-existence of a passenger in a passenger seat in an automobile and for controlling the expansion of an air bag in an air bag system based on the detection result.
2. Description of the Related Art
Generally, an air bag system is a system to protect a driver of an automobile from the impact when an automobile collides. Recently, the air bag system is installed for a passenger in addition to a driver. Thus, even if the automobile collides, the passenger on the passenger seat can be protected from the impact on the collision by the expanding operation of the air bag in addition to the driver.
As shown in FIG. 1, an air bag system is composed of a squib circuit on the side of a driver seat, a squib circuit on the side of a passenger seat, an electronic acceleration sensor (a collision detecting sensor) GS and a control circuit CC. The squib circuit on the side of the driver seat is composed of a series circuit of a safing sensor SS1, a squib SQ1, and a semiconductor switching element SW1 such as a field effect transistor. The squib circuit on the side of the passenger seat is composed of a series circuit of a safing sensor SS2, a squib SQ2, and a semiconductor switching element SW2 of a field effect transistor. The control circuit CC detects collision in response to an output signal of the electronic acceleration sensor GS and supplies detection signals to the gates of the semiconductor switching elements SW1 and SW2.
According to the air bag system, when the automobile collides because of any cause, the switch contacts of the safing sensors SS1 and SS2 respond to the relatively small acceleration to be closed. The squib circuit on the side of the driver seat and the squib circuit on the side of the passenger seat are set to the operable state. When the control circuit CC determines the collision of the automobile in response to an acceleration detection signal from the electronic acceleration sensor GS, the control circuit CC supplies the detection signals to the gates of the semiconductor switching elements SW1 and SW2. As a result, the switching elements SW1 and SW2 are set to the ON state. Thus, current flows through each squib circuit. In this way, the air bag on the side of the driver seat and the air bag on the side of the passenger seat are expanded because of heat generation by the squibs SQ1 and SQ2 to protect the driver and the passenger from the impact due to the collision.
By the way, in this air bag system, an air bag is expanded irrespective of existence or non-existence of the passenger on the passenger seat, when the automobile collides. Therefore, when the passenger has sat on the passenger seat, the protection effect of the passenger can be expected upon the collision. In this case, however, when the passenger is not on the passenger seat, the expansion of the air bag does not have any meaning and a repair expenses to restore the air bag becomes necessary. Therefore, it is preferable that a passenger detecting system determines whether or not a passenger is on the passenger seat, and the expansion operation of the air bag system is performed upon the collision, only when the passenger is on the passenger seat.
In order to solve the above problem, an air bag system as shown in FIG. 2 is proposed. In the air bag system shown in FIG. 2, a sensor SD is provided to determine whether or not a passenger is on the passenger seat, and the control circuit CC determines that the passenger is on the passenger seat, based on a detection signal of the sensor SD. Thus, an air bag is set to an either of the expansion allowed state in which it is expanded when the automobile collides or the expansion inhibited state in which it is not expanded even when the automobile collides.
As the passenger detecting system to detect the existence or non-existence of the passenger on the passenger seat are proposed various systems. In Japanese Laid Open Patent Application (JP-A-Heisei 4-46843), Japanese Laid Open Utility Model Application (JP-U-Heisei 3-52266), Japanese Laid Open Patent Application (JP-A-Showa 61-113527), a passenger detecting system in which a weight sensor is incorporated inside the seat is disclosed. Also, in Japanese Laid Open Patent Application (JP-A-Heisei 9-509118), a passenger detecting system in which electrodes are arranged in a seat section and a back supporting section of a seat and an oscillation circuit is connected between the electrodes or between the electrode and the chassis of a vehicle.
According to the former passenger detecting system, the weight sensor does not respond when anybody or anyone is not on the passenger seat. Thus, the existence or non-existence of the passenger on the passenger seat can be detected by the weight sensor. Also, according to the latter passenger detecting system, a capacitance increases between the electrodes or between the electrode and the chassis of the automobile when the passenger is on the seat. The passenger detecting system using the weight sensor is possible to perform the rough determination of whether the passenger on the passenger seat is an adult or a child. An air bag is set to either of the expansion allowed state or the expansion inhibited state, based on the determination result. Thus, an unexpected situation upon the collision of the automobile can be avoided. However, the weights are quite different between individuals and a child can be sometimes heavier than an adult. Therefore, the passenger detecting system using the weight sensor lacks of accuracy.
On the other hand, the capacitance decreases when any passenger is not on the passenger seat. The change of an oscillation frequency due to the change of the capacitance is detected using this phenomenon and the existence or non-existence of the passenger on the passenger seat can be detected. Also, when the passenger is not on the passenger seat, the expansion operation of the air bag system can be prevented, unlike the conventional air bag system. However, the electrode 4 is connected to a cable 106 using a connector 110. Therefore, there is a problem that the work efficiency is low and the reliability is low.
In addition to the technique using a sensor detecting the weight of a passenger, there is known the technique in which the passenger is picked up by a camera and determinations of whether the existence or non-existence of the passenger is on the passenger seat, and whether the passenger is a adult or a child are performed through an image processing. Thus, in case of the passenger detecting system using a camera, the existence or non-existence of the passenger, and the adult or the child can be quite correctly determined. However, because a passenger pattern must be determined from various data obtained by processing the imaging data which has been taken by the camera, a processor becomes complicated and expensive.